The present invention relates to a windshield wiper arrangement for motor vehicles with a wiper arm that rests on the surface to be cleaned with a variable abutment force dependent on the vehicle velocity.
It is known in principle from the DE-PS No. 31 48 253 to adjust the abutment force dependent on the vehicle velocity. Furthermore, it is known from the DE-AS No. 23 14 724 to variably adjust the abutment force corresponding to the contour of the surface to be cleaned.
The present invention is concerned with an improvement of the windshield wiper arrangement disclosed in the DE-PS No. 31 48 253. In particular, the present invention keeps the wiper arm, already on the surface to be cleaned at the beginning of the operation, at a sufficient abutment pressure, to assure, with an additional washing operation a reliable cleaning of the surface. The underlying problems are solved according to the present invention in that the abutment force is increased compared to the standing-still motor vehicle and the abutment force during non-wiper operation is smaller than during wiper operation and/or in case of additional washing operation is larger than during wiper operation.
The present invention starts with the recognition that the adjustment of the abutment force requires a certain time. If increasing the abutment force to the necessary value are initiated at the beginning of the wiper operation, then this leads to a wiper operation with insufficient abutment pressure during the first wiping cycle and during slower build-up of the abutment force during a few wiping cycles. Since the wiping operation is engaged, as a rule, only when urgently needed, this leads, in particular at high vehicle velocities, to an unsafe situation. Thus, only after an excessively long period of time a considerable distance, can reckon with a sufficient cleaning action is achieved.
The same is true during the engagement of the washing operation in addition to the wiper operation. By the application of an increased liquid quantity, it is necessary to provide a sufficiently large abutment force because only in that case is an adequate cleaning action assured. Since the build-up of the abutment force is slow, the abutment force is not adequate during the starting phase of the wiper/washing operation. The consequences are equally critical as in the previously described case at the beginning of the pure wiper operation.
It is achieved by the present invention that at the beginning of the wiper operation and/or of the additional washing operation, the abutment force has the requisite abutment magnitude. Thus during the first wiping cycle, an adequate cleaning action is assured. The traffic safety is considerably increased thereby.
Further features of the present invention are directed to the adjustment of the abutment force in two or three steps. In the two step case, the transition between the steps takes place during wiper operation as a function of velocity. During non-wiper operation, the low base step as regards abutment force is always engaged. With additional operation, the higher maximum step as regards abutment force is always engaged.
For the adjustment of the abutment force in three steps, the adjustment of the abutment force during wiper operation is undertaken dependent on the velocity and includes a middle step which, compared to the base step, has a greater abutment force and compared to the maximum step, a lower abutment force. The base step is engaged during non-wiper operation also at a vehicle velocity, at which during wiper operation the middle or the maximum step is engaged. During washer operation, the middle and/or the maximum step is engaged at a vehicle velocity at which, during wiper operation, the base and/or middle step respectively is engaged.
It is common to both further features that the adjustment of the abutment force takes place in steps which are dependent on the vehicle velocity. During non-wiper operation, the engaged step, insofar as this is possible, is reduced with respect to the wiper operation by one, respectively, possibly also by the two steps in the csse of three steps. During washing operation, the adjustment of the abutment force is increased inversely by one, respectively, by two steps compared to the pure wiper operation. A possibly necessary increase of the abutment force takes place then as a rule only by one step. The time necessary therefor is noticeably reduced compared to the adjustment of the abutment force to the required strength only in the case of need and starting from the level with standing motor vehicle.